There is a need to provide methods for utilizing heat from sources that are heretofore generally referred to as waste heat. Such methods would provide a more efficient use of resources, reduce the emissions of products of combustion, and minimize the increase of temperature of the environment, e.g. air and water. For example, in many power stations, power houses and the like, fuels are burnt to provide hot gases. The hot gases are used to turn gas turbines, convert water into steam to turn steam turbines, or perform other useful work. However, not all of the heat from the burned fuel can be converted into useful work and the gases are vented to the atmosphere while they are still warm. The heat in the vented gases is sometimes referred to as waste heat. Heretofore, it has been difficult to recover waste heat and convert a part of it to useful work because such conversion is less efficient at lower temperatures. Accordingly recovery of waste heat to power is not common.
In some industrial operations such as furnace operations in a building in which the furnace is housed, the air in the building tends to get very hot. For the comfort and safety of workers in the building it is important to extract the hot air from the building. In the past this has been done by extracting the hot air using fans. It is usual for such fans to be electrically driven. Fuel is used in electricity generating stations to generate such electricity. If it would be possible to operate the fans without such electrical consumption there would be savings in the purchase of electrical power. In addition, there would be a net positive effect on the environment in terms of fewer emitted pollutants, e.g. carbon dioxide, sulphur dioxide, nitrogen oxides, particulates and the like associated with power plant operations.
The present invention seeks to provide a method for providing a self-propelled exhaust fan by recovering heat from warm exhaust gases and converting some of the heat to shaft power to drive the fan. The invention also seeks to provide a method for recovery of work from relatively low temperature fluids, e.g. waste heat.